1. Field of the Invention
The present invention relates to architectural devices and, more specifically, a shadow box for use in various building cladding systems including but not limited to unitized and stick system curtain wall, window wall, strongback, punched windows and other framed assemblies and rain screen assemblies.
2. Description of the Related Art
A curtain wall is a non-structural outer covering of a building. A curtain wall serves to provide a desired exterior appearance and to keep exterior environmental elements (e.g., wind, rain, etc.) out of the building. While a curtain wall will impart horizontal forces, such as wind loading, to the structural elements of the building, it does not bear the vertical load of the building (except for its own dead weight). Because it is non-structural, it provides a relatively inexpensive way to finish a building's exterior.
A typical enclosure system such as a curtain wall includes an array of mullions, which are vertical and horizontal elements that hold transparent vision glass and opaque spandrel zones. A typical spandrel zone can consist of the following components: a facing material (such as, aluminum, stone, glass masonry, etc.), insulation, and an air and vapor barrier.
The requirements for thermal insulation and fire separation dictate the need for opaque spandrel panels. In addition, other elements that are not desired to be seen are typically concealed by a opaque panels that can be identical to the spandrel or made of other materials. One way to hide such elements is by substituting opaque glass over the elements to be hidden. However, this approach interrupts the visual effect of the vision glass spandrels, which can be an aesthetically undesirable effect.
To give the illusion of depth, some architects design curtain walls in which the elements to be hid are covered with shadow boxes. A shadow box is a spandrel with a vision glass exterior and an opaque back that is offset by several inches from the vision glass exterior. The opaque back hides the elements to be hidden, while the visual effect of the offset can appear similar to the vision glass glazing of the rest of the curtain wall.
Some shadow boxes are deliberately vented to the exterior of the building, some are inadvertently vented to the interior of the building and some are deliberately fully sealed. If they are vented to the exterior, it is possible for dust, insects and the like to enter the shadow box. It is also possible for condensation to form within the shadow box during hot and humid weather. If they are vented to the interior there may be a pathway for dust to form on the inner (#2) surface of the glazing. During cold weather, there is also a high possibility for condensation to form within the spandrel box. If they are fully sealed and moisture enters the spandrel box, either through faults in the inner or outer seals, then long-term condensation may occur. Dust and dirt collection within a spandrel box, the presence of insects and the like within a spandrel box and the presence of condensation within a spandrel box can all be considered as failures of the spandrel box. Opening an installed shadow box to clean it is not a practical solution to problems involving dirt and moisture.
Another form of shadow box uses a conventional insulating glass unit with a solid frit or coating on the innermost surface of the glass. This system addresses the visual problems of the standard spandrel box solution described above by visually blocking any dirt, dust, insects and the like, and condensation that may form in externally or internally vented or fully sealed shadow boxes. This form of shadow box does not provide the visual depth often desired by the designer. In addition, this form of shadow box may not prevent condensation formation (and it prevents the visual warning that condensation may be forming). Such condensation may lead to failures of the shadow box.
Cladding system like curtain walls can be constructed on-site (in which case they are referred to as “stick systems”) or they can be assembled in panels at a unitized assembly shop as part of unitized systems such as unitized curtain walls that are shipped to the construction site. In both cases, shadow boxes are constructed as part of the construction of the panels of the curtain wall. This makes curtain wall construction a time consuming process. Also, since the shadow boxes are constructed on an ad hoc basis, ensuring that their seals and tolerances are suitable for long duration construction can be difficult. Multiple decades of ad hoc shadow box construction has demonstrated that it is hard to achieve an effective hermetic seal into a shadow box made this way. Additionally, when constructing shadow boxes on-site and at unitized assembly shops typically results in the introduction of dust and other impurities into the shadow box, which detracts from the visual effect of the shadow box.
Therefore, there is a need for a prefabricated shadow box unit that employs seals with a long lifetime.